Mount the hook and start thread mid-shank. Figure-8 the dumbbell eyes on top near the bend so the fly rides hook-point-up when weighted.
At the rear, tie in two small splayed clumps of tan craft fur as claws, one shank length long, with a few strands of flash between.
Add three pairs of barred rubber legs splayed to the sides across the middle of the shank.
Spin or stack tan EP fiber/craft fur around the shank and pack it tight to build a flat oval carapace, working forward to the eyes.
Trim the body top and bottom into a flat crab-shell shape, leaving it wide and low-profile.
Tie in a doubled hard-mono weed guard at the eye, then build a neat head and whip finish. Cast ahead of cruising redfish and permit and let it drop to the bottom, then give short strips to hop it like a fleeing crab.